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High-resolution Record (high-resolution + record)
Selected AbstractsHigh-Resolution Records of the Holocene Paleoenvironmental Variation Reflected by Carbonate and Its Isotopic Compositions in Bosten Lake and Response to Glacial ActivitiesACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 6 2009ZHANG Chengjun Abstract: The Early Holocene paleoclimate in Bosten Lake on the northern margin of the Tarim Basin, southern Xinjiang, is reconstructed through an analysis of a 953 cm long core (BSTC2000) taken from Bosten Lake. Multiple proxies of this core, including the mineral components of carbonate, carbonate content, stable isotopic compositions of carbonate, Ca/Sr, TOC and C/N and C/S of organic matter, are used to reconstruct the climatic change since 8500 a B.P. The chronology model is made by nine AMS 14C ages of leaves, seeds and organic matter contained in two parallel cores. The climate was cold and wet during 8500 to 8100 a B.P. Temperature increased from 8100 to 6400 a B.P., the climate was warm and humid, and the lake expanded. The lake level was highest during this stage. Then from 6400 to 5100 a B.P., the climate became cold and the lake level decreased slightly. During the late mid-Holocene, the climate was hot and dry from 5100 to 3100 a B.P., but there was a short cold period during 4400 to 3800 a B.P. At this temporal interval, a mass of ice and snow melting water supplied the lake at the early time and made the lake level rise. The second highest lake level stage occurred during 5200 to 3800 a B.P. The climate was cool and wet during 3100 to 2200 a B.P., when the lake expanded with decreasing evaporation. The lake had the last short-term high level during 3100 to 2800 a B.P. After this short high lake level period, the lake shrank because of the long-term lower temperature and reduced water supply. From 2200 to 1200 a B.P., the climate was hot and dry, and the lake shrank greatly. Although the temperature decreased somewhat from 1200 a B.P. to the present, the climate was warm and dry. The lake level began to rise a little again, but it did not reach the river bed altitude of the Konqi River, an outflow river of the Bosten Lake. [source] Stomatal evidence for a decline in atmospheric CO2 concentration during the Younger Dryas stadial: a comparison with Antarctic ice core recordsJOURNAL OF QUATERNARY SCIENCE, Issue 1 2002J. C. Mcelwain Abstract A recent high-resolution record of Late-glacial CO2 change from Dome Concordia in Antarctica reveals a trend of increasing CO2 across the Younger Dryas stadial (GS-1). These results are in good agreement with previous Antarctic ice-core records. However, they contrast markedly with a proxy CO2 record based on the stomatal approach to CO2 reconstruction, which records a ca. 70 ppm mean CO2 decline at the onset of GS-1. To address these apparent discrepancies we tested the validity of the stomatal-based CO2 reconstructions from Kråkenes by obtaining further proxy CO2 records based on a similar approach using fossil leaves from two independent lakes in Atlantic Canada. Our Late-glacial CO2 reconstructions reveal an abrupt ca. 77 ppm decrease in atmospheric CO2 at the onset of the Younger Dryas stadial, which lagged climatic cooling by ca. 130 yr. Furthermore, the trends recorded in the most accurate high-resolution ice-core record of CO2, from Dome Concordia, can be reproduced from our stomatal-based CO2 records, when time-averaged by the mean age distribution of air contained within Dome Concordia ice (200 to 550 yr). If correct, our results indicate an abrupt drawdown of atmospheric CO2 within two centuries at the onset of GS-1, suggesting that some re-evaluation of the behaviour of atmospheric CO2 sinks and sources during times of rapid climatic change, such as the Late-glacial, may be required. Copyright © 2002 John Wiley & Sons, Ltd. [source] Redating the onset of burning at Lynch's Crater (North Queensland): implications for human settlement in AustraliaJOURNAL OF QUATERNARY SCIENCE, Issue 8 2001C. S. M. Turney Abstract Lynch's Crater preserves a continuous, high-resolution record of environmental changes in north Queensland. This record suggests a marked increase in burning that appears to be independent of any known major climatic boundaries. This increase is accompanied, or closely followed, by the virtually complete replacement of rainforest by sclerophyll vegetation. The absence of any major climatic shift associated with this increase in fire frequency therefore has been interpreted as a result of early human impact in the area. The age for this increase in burning, on the basis of conventional radiocarbon dating, was previously thought to be approximately 38 000 14C yr BP, supporting the traditional model for human arrival in Australia at 40 000 14C yr BP Here we have applied a more rigorous pre-treatment and graphitisation procedure for radiocarbon dating samples from the Lynch's Crater sequence. These new dates suggest that the increase in fire frequency occurred at 45 000 14C yr BP, supporting the alternative view that human occupation of Australia occurred by at least 45 000,55 000 cal. yr BP. Copyright © 2001 John Wiley & Sons, Ltd. [source] THE SHAPE OF THE PHANEROZOIC MARINE PALAEODIVERSITY CURVE: HOW MUCH CAN BE PREDICTED FROM THE SEDIMENTARY ROCK RECORD OF WESTERN EUROPE?PALAEONTOLOGY, Issue 4 2007ANDREW B. SMITH Abstract:, Palaeodiversity curves are constructed from counts of fossils collected at outcrop and thus potentially biased by variation in the rock record, specifically by the amount of sedimentary rock representative of different time intervals that has been preserved at outcrop. To investigate how much of a problem this poses we have compiled a high-resolution record of marine rock outcrop area in Western Europe for the Phanerozoic and use this to generate a model that predicts the sampled diversity curve. We find that we can predict with high accuracy the variance of the marine genus diversity curve (itself dominated by European taxa) from rock outcrop data and a three-step model of diversity that tracks supercontinent fragmentation, coalescence and fragmentation. The size and position of two of the five major mass extinction spikes are largely predicted by rock outcrop data. We conclude that the long-term trends in taxonomic diversity and the end-Cretaceous extinction are not the result of rock area bias, but cannot rule out that rock outcrop area bias explains many of the short-term rises and falls in sampled diversity that palaeontologists have previously sought to explain biologically. [source] Mangshan Loess in Central China and the Paleomonsoon Variations since the Last InterglaciationACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 3 2004JIANG Fuchu Abstract, The Mangshan Yuan is a loess platform on the southern bank of the Yellow River, which is located in northwestern Zhengzhou of Henan Province, China. The typical Zhaoxiayu section of the Mangshan Yuan preserves stratigraphical loess units above S10 with a total thickness of 172.1 m, which includes 15.7 m of the last interglacial paleosol S1, 77.3 m of the last glacial loess L1 that consist of 41.6 m of the late stade L1LL1, 13.2 m of the interstade L1SS1 and 22.5 m of the early stade L1LL2. Based on the age marking points by correlating magnetic susceptibility of the section with the SPECMAP curve, the timescale of the section was constructed, and the average accumulation rate and the resolution of each loess strata over the S2 were subsequently calculated using the susceptibility age model. The results indicate that strata units developed in the glacial, interglacial stages, stadial and interstadial show substantial differences in grain size, average accumulation rate and time resolution ub the Zhaoxiayu section. Specifically, the average accumulation rate of the loess L1LL1 is 3.45 mm/a, whereas that of paleosol S1 is only 0.28 mm/a. Based on the high-resolution records of magnetic susceptibility and >45 ,m fraction percentage of the loess-paleosol, the summer and winter monsoon variations as well as their interrelations since the last interglaciation have been discussed, which were correlated with the SPECMAP and the GRIP climate records. [source] | ||||||||||